Suspension systems and more particularly vehicle and bicycle suspension systems have been available for many years. The predominant form of vehicle suspension, and more specifically, bicycle suspension dampers, are telescopic. Suspension systems typically comprise a spring for energy storage and a damping mechanism for energy dissipation. Suspension systems are used to absorb impact and/or vibration in a wide variety of configurations including vehicle seats, vehicle wheels, industrial machinery, watercraft hull/cabin or cockpit interface, bicycle seat posts and many others. Vehicle wheel suspension often includes a damping mechanism for dissipating energy (from wheel movement caused by disparities in the terrain over which the vehicle travels) and a spring mechanism for storing energy for rebound. Damping assemblies often convert wheel movement into heat by means of fluid friction in a fluid filled dashpot (piston and cylinder) type damping device. Spring mechanisms may take many forms including, coiled springs, elastomer bumpers, compressible fluid (e.g. gas, silicone oil), suitable combinations thereof or other suitable energy storage mechanisms. Two wheeled vehicle front forks and rear shocks are designed such that a dampening piston is slidably contained within a cylinder. The cylinder typically contains a damping fluid (e.g. liquid oil) or fluids and the piston typically includes a valve or orifice through which the fluid flows from one side of the piston to the other as the piston moves axially within the cylinder. In typical bicycle suspension forks there are two cylinders and two pistons with one each paired telescopically on either side of a front wheel. Bicycle suspension forks are described in U.S. Pat. Nos. 6,217,049 and 5,186,481, each of which patents is incorporated herein, in its entirety, by reference. A bicycle rear shock unit is described in U.S. Pat. No. 7,147,207 which is incorporated herein, in its entirety, by reference.
When a bicycle is equipped with front or rear suspension or both, it will tend to “bounce” in response to the cyclical force exerted on the pedals. There a couple of reasons for that but the result of any bounce is power loss. Suspension “squat” power loss on motorized vehicles may not be significant because the horsepower available is often more than adequate to compensate for the loss while still providing ample usable power. That may not be true of human powered vehicles such as bicycles. A typical adult human in good physical condition can supply approximately one half horsepower to the peddle crank of a bicycle. An elite athlete may supply horsepower approaching 0.6. In any case that isn't much horsepower and any loss is usually noticeable.
Another power loss mechanism involved is that of “chain power squat.” When, for example, a chain exerts a forward directed pulling force on the rear sprocket of the bicycle, that force vector will tend to upwardly rotate a rear suspension swing arm about its pivot point at the frame connection if the chain, as it runs between the drive (chain ring) and driven (rear) sprockets, extends above the pivot point. Most often the chain does run above the pivot point and as force is exerted on the chain some of the force is expended in compressing the rear suspension (as the swing arm rotates due to the chain moment).
Another power loss mechanism is the force induced bounce that directly results from the rider's interaction with the pedals. A bicycle rider can usually exert more force downwardly on a pedal than upwardly. That means that the maximum force exerted on the bicycle power crank moves alternately from side to side of the bicycle laterally, as each pedal is pushed through a down stroke. The asymmetric and cyclical nature of the peddling action induces some bounce in both front and rear suspension units on a bicycle. As previously discussed, compression of suspension requires power. That power comes from one source on a bicycle and that is the rider.
In order that a bicycle rider may maximize the power delivered to driving the bicycle forward and minimize suspension compression waste (due to pedal “bob” and/or “squat”), there is a need for suspension units that can act as rigid units when suspension characteristics are not required, yet act to provide shock absorption when needed.
As previously mentioned, vehicle suspension systems are often damped by means of a piston traversing a liquid (e.g. hydraulic oil) filled cylinder arrangement. In such arrangement the piston is forced, alternatingly by terrain induced compressive loads and spring induced extension loads, through the liquid filled cylinder in response to operation of the suspension. Impact energy imparted to the suspension by terrain variation is dissipated by the damping system in the form of heat. Heat, generated by friction between the damping fluid and the traversing piston, builds up in the damping fluid and surroundings as the suspension is cycled. When the suspension is used vigorously, the heat build up can exceed the natural rate of heat transfer from the suspension to the surrounding atmosphere. Such heat build up can adversely affect the operation of the suspension damper. For example, the heat build up in the damping liquid will correspondingly change (e.g. lower) its viscosity and/or shear strength. Such changes can affect the damping force generated (and energy dissipation) by the damping piston during operation and may render the damping mechanism ineffective.
Accordingly there is a need for a selectively rigid suspension unit. Further, there is a need for a suspension unit that can be placed in a rigid condition without relying on hydraulic or other fluid lock out. There is a need for a vehicle suspension having increased heat dissipation characteristics. Further there is a need for a vehicle suspension unit that can convert vehicle movement to electric power. Further there is a need for a vehicle suspension unit that can use power generated therein to increase performance of the suspension.